1. Field of the Invention.
The field of the invention is prosthetic devices and, in particular, prostheses for replacing segments of blood vessels of the body.
2. Description of the Related Art
Vascular prostheses (i.e., artificial blood vessels) are used to replace diseased arteries or to provide access to blood by connecting a patient's artery to a vein. Vascular graft prostheses must be porous and made of a biocompatible material. The luminal surface must be thromboresistant and heal with a neointima or a pseudointima. This neointima must remain thin and not proliferate, to prevent eventually occluding the prosthesis. This physiological healing also helps prevent infection and transient occlusions.
Vascular prostheses undergo cyclic loading in response to cardiogenic blood pressure changes. As a consequence, the prostheses must be able to withstand fatigue. In addition, prostheses are sometimes under tensile stress intraoperatively when they are pulled subcutaneously. Normally, the tensile stress is minimal after completing the anastomosis. Nevertheless, tensile forces are exerted during kinking, when a prostheses is placed around a joint. Kink resistance is a desirable feature when placing a prostheses intraoperatively, in order to assure a patent lumen.
Compliance is another desirable feature of a vascular prosthesis. Compliance is the ability to expand and contract like a natural artery in response to changing blood pressure. Matching compliance of the prostheses with the compliance of the natural artery at the anastomosis is one of the most important requirements for long-term success of a small diameter vascular graft prosthesis. Without compliance, turbulence develops at the suture lines, causing intimal hyperplasia. Vascular prostheses should be designed to be isocompliant with the attached artery.
Various approaches have been taken to providing vascular graft prostheses. Some prostheses are hybrids of natural and artificial components. For example, U.S. Pat. No. 4,546,500 to Bell discloses a method and apparatus for producing living blood vessels that incorporates a plastic mesh sleeve within the layers of the vessels. U.S. Pat. No. 3,626,947 to Sparks and U.S. Pat. No. 4,743,251 to Barra disclose methods for reinforcing veins and arteries with multiperforated flexible sheaths or textile mesh reinforcing tubes.
Other prostheses are wholly artificial. For example, U.S. Pat. No. 4,657,544 to Pinchuk describes a porous elastic cardiovascular graft without any wrap or exterior structure to provide strength or kink resistance. U.S. Pat. No. 2,990,605 to Demsyk describes an artificial vascular member that is formed from a Dacron tube but does not appear to be compliant. U.S. Pat. No. 4,610,688 to Silvestrini, et al. describes triaxiallybraided fabric vascular prostheses that may be made to be flexible in both longitudinal and radial directions, but does not have any exterior reinforcement for kink resistance or the like. U.S. Pat. No. 4,286,341 to Greer, et al. provides a vascular prosthesis with a woven or knitted support tube made from Dacron or other biocompatible fiber-forming materials. U.S. Pat. No. 4,550,447 to Seiler, Jr., et al. provides a vascular graft prosthesis with a porous tube reinforced by generally transverse external ribs. U.S. Pat. No. 3,479,670 to Medell discloses a tubular prosthetic implant composed of a knitted fabric tube wrapped with helical thermoplastic monofilament. U.S. Pat. No. 4,604,762 to Robinson discloses an arterial graft prosthesis that may be provided with a confining netting of Dacron or the like which loosely surrounds the remainder of the artificial artery in order to confine substantial expansions of the artificial artery.
As may be seen from the above survey, various approaches have been taken to provide completely or partially artificial vascular graft prostheses that have some, but not all, of the features of living blood vessels. Generally, a porous and flexible tube is provided to contain blood elements. A porous (necessary for ingrowth of surrounding tissue) wrap may be provided for radial and longitudinal strengthening and possibly for kink resistance. The tube may expand and contract in some of the prostheses, such as those of Pinchuk, Silvestrini, et al., and Robinson described above.
Currently available wraps on vascular prostheses provide radial and tensile strength and, in some cases, kink resistance. No wraps, apart from those of Robinson (U.S. Pat. No. 4,604,762), are known that also allow for compliance because existing wraps are in intimate contact with the walls of the vascular prostheses. Consequently, they restrict the expansion due to increasing blood pressure.
A need exists, therefore, for a vascular graft with a wrap which permits the graft to be compliant while providing radial and longitudinal strengthening and resistance to kinking.